The long-term goal of the research described here is to elucidate the mechanisms by which eucaryotic cells coordinate the expression of specific sets of genes during development. The proteinaceous eggshell of Drosophila melanogaster is composed of four distinctive layers whose synthesis and assembly is sequentially carried out by the follicular epithelium. Since at least 24 different proteins are involved in the various layers, eggshell development requires a mechanism to temporally coordinate the expression of not one but a set of developmentally related genes. It is the nature of this developmental control mechanism that we want ultimately to elucidate. We believe that a key problem in the understanding of this control mechanism is to determine the detailed chromosomal arrangement of the genes, both structural and regulatory, involved in Drosophila eggshell development. To this end we propose (1) to continue and expand a successful initial study utilizing diverse natural populations of Drosophila as a source of electrophoretically variant eggshell proteins that have allowed us to genetically map some of the major eggshell genes; (2) to complement our genetic localization studies with studies involving the in situ hybridization of chorion cDNAs cloned in bacterial plasmids. As the chromosomal locations are established, we propose to initiate studies to carefully examine these genetic areas and the role played by their gene products in eggshell development by analyzing the effect of perturbing these locations where possible with deletions and other mutations. As important complementary studies, we also propose to continue studies on the biochemistry and morphology of normal and mutant eggshells utilizing new techniques developed in our laboratory for (1) the more precise identification of true minor eggshell components; (2) the determination of differences in the composition of the shell in its specialized regions (operculum, respiratory appendages and posterior pole) as compared to the mainshell; and (3) the identification and characterization of the proteins of the heretofore poorly studied (biochemically) layers of the shell, the vitelline membrane and innermost chorionic layer.